Lead-Free (1 - x)Ba(Zr_0.2Ti_0.8)O₃ - x(Ba_0.7Ca_0.3)TiO₃‑Based Ferroelectrics with Diffuse Phase Transitions for...

The electrocaloric effect of a ferroelectric material is an effective technique for solid-state refrigeration. Although the peak value of the adiabatic temperature change (ΔT) due to the electrocaloric effect in normal ferroelectrics is found near the Curie point (T _c), ferroelectrics with a diffuse phase transition are always desirable due to their wide temperature span of ΔT. In this work, the electrocaloric effect in sustainable Pb-free weak relaxor ferroelectrics, (1 - x)-Ba-(Zr_0.2Ti_0.8)-O₃ - x(Ba_0.7Ca_0.3)-TiO₃ (x = 0.19 and 0.21), with diffuse phase transition is reported. The diffuseness of each composition is determined based on the fitting of the temperature-dependent dielectric permittivity data to the Lorenz-type quadratic law. Interestingly, the maxima of ΔT of the compositions are observed at much higher temperatures than the temperature at maximum dielectric permittivity (T _m) and freezing temperature (T _f), which work as the effective T _c of a relaxor ferroelectric. The wide temperature span (40 K) and high ΔT (0.8 K) of the x = 0.19 composition show the potential of this material for solid-state refrigeration applications. Moreover, the effects of diffuse phase transition on ΔT and its temperature span are discussed in (1 - x)-Ba-(Zr_0.2Ti_0.8)-O₃ - x(Ba_0.7Ca_0.3)-TiO₃-based ferroelectrics, which will help to design Pb-free electrocaloric materials with a diffuse phase transition for a wide working temperature range.